Microdeposition system for a biosensor

ABSTRACT

A microdeposition pin having a contact surface with at least one concave edge for creating microarrays and the like. The microdeposition pin may be used either alone or with a plurality of microdeposition pins in conjunction with a holder. The concave edge of the pin is especially adapted for helping to control the spreading of a deposited material. By selectively controlling the spread of the reagent composition from the microdeposition pin, the flow of the reagent composition from the deposition target area may be reduced. Sensor strips having raised substrate features with limited or no spreading of the reagent composition beyond the target area are disclosed.

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/942,437 entitled “Microdeposition System For A Biosensor” filed Jun.6, 2007, which is incorporated by reference in its entirety.

BACKGROUND

Microarray biosensors for biological analysis are well known in the art.Generally, a biochemical substance, such as multiple droplets of areagent, is deposited onto a substrate to form the microarray. Eachdroplet of the reagent is preferably in electrical communication with anelectrode so as to form an individual biosensor. The droplet of reagentmay then be exposed to a biological agent or the like, such that areaction is caused. With the aid of at least one additional electrode,various factors of the reaction may be measured and/or observed toprovide the analysis.

Various techniques may be used to create the microarray biosensors, suchas screen printing, ink-jetting, micro-pipetting, and pin-deposition.Each of the techniques have advantages. For instance, screen printingmay be preferred when a relatively large deposit of a thick reagentlayer is required to control spreading of the reagent composition.“Spreading” refers to the outward flow of a deposit of material due tothe material's viscosity. Screen printing also may be preferred due tothe high speed at which deposition may occur. If smaller area depositsare desired, ink-jetting, micro-pipetting, or pin-deposition may bepreferred. These techniques can more precisely control the volume of areagent composition deposited onto a substrate.

In contrast to screen printing, ink-jetting and micro-pipetting arenon-contact techniques, where only the reagent composition contacts thesubstrate. While ink-jetting can deposit very small volumes of thereagent composition with little spreading, the method cannot effectivelydeposit biomolecules due to the small size of the individual dropletssprayed by the print head, approximately 10 to 100 picoliters (pL).Furthermore, biomolecules, especially those of high molecular weight,may lead to clogging of the deposition nozzle. Micro-pipetting candeposit very small volumes of the reagent composition, but spreading isinfluenced by the flow of the reagent composition liquid over thetopography of the substrate. If the substrate has raised areas formed byconductors or other features, the reagent composition may flow from theraised areas into lower areas providing more undesirable spreading fromthe deposition area. As with ink-jetting, biomolecules in the reagentcomposition also may clog the pipette.

With pin-deposition, one or more microdeposition pins contact thesubstrate to transfer the reagent composition. Pin contact with thesubstrate allows for the transfer of relatively small volumes of reagentcomposition while reducing spreading of the reagent composition fromraised features. Thus, pin-deposition may provide thin reagent layersfrom small deposition volumes while maintaining liquid controladvantages.

Pin-deposition generally starts by lowering multiple pins into a sourceplate having wells containing a reagent composition. As the pins aredipped into the wells, they are coated with the reagent. The pins aremoved above the substrate, and the reagent is transferred from the pinsto the substrate during a brief touchdown. Pin-deposition also allowsthe force with which the pin contacts the substrate to be altered.

Conventional deposition pins generally are quill or solid in design.Quill pins differ from solid pins in that quill pins include a narrowslit at the tip of the pin. This slit acts as a fluid reservoir, whichholds the reagent composition before the pin contacts the substrate.Each time a quill pin contacts the substrate, it deposits at least aportion of the reagent composition from the reservoir. The reservoir isgenerally sized to hold sufficient volume of reagent for multipledepositions.

Solid microdeposition pins generally have small, flat tips that aredipped into the reagent composition before each contact with thesubstrate. As the reagent composition flows down the exterior sides ofthe pin, there is no passageway for biomolecules and other highmolecular weight constituents to clog. The volume and morphology of theresulting deposition spot may depend on the diameter of the solid pintip, the surface tension of the reagent composition, and the hydrophobiccharacter of the substrate in relation to the hydrophilicity of thereagent composition. For example, a 0.2 millimeter (mm) diameter pin mayproduce depositions having a diameter of approximately 400 micrometers(μm). When depositing solution volumes of from 10 picoliters (pL) to 10nanoliters (nL), the 0.2 mm diameter pins may provide deposition areashaving diameters ranging from 100 μm to 1,000 μm. Conventional solidpins having tips that are either round or square are known to producesubstantially round deposition areas.

However the biosensors are manufactured, they may be used for analysisof a biological fluid, such as whole blood, urine, or saliva. Typically,biosensors have a measurement device that analyzes a sample of thebiological fluid placed on a sensor strip. The analysis may determinethe concentration of one or more analytes, such as alcohol, glucose,uric acid, lactate, cholesterol, or bilirubin, in the biological fluid.The analysis is useful in the diagnosis and treatment of physiologicalabnormalities. An ongoing need remains for microdeposition techniquesthat provide enhanced control over the spreading of the depositedreagent composition.

SUMMARY

A microdeposition system includes one or more microdeposition pin with apolygonal cross-section contact surface and one or more concave orsubstantially flat exterior edge. The microdeposition pins reduce oralter the spreading of a reagent composition away from the concaveand/or substantially flat exterior edges of the pin. The pins also mayreduce or alter the amount of the reagent composition that flows past animaginary line extending between adjacent edges of a concave edge of thepin.

A microdeposition pin for microprinting includes a shaft terminating ina head having a polygonal cross-section with at least one concaveexterior surface. The pin may have at least two concave exteriorsurfaces, at least three concave exterior surfaces, at least two concaveexterior surfaces and at least two convex exterior surfaces, or at leastone substantially flat exterior surface. The concave exterior surfacemay form an external reagent composition reservoir. The cross-sectionalarea of the concave exterior surface may be less at the head than higheron the shaft. The concave exterior surface of the pin may extend fromabout 2 mm to about 8 mm from the head along a longitudinal direction ofthe shaft, and the shaft may taper toward the head, the shaft and thehead may have substantially the same radius.

The microdeposition pin may have a maximum cross-sectional head diameterfrom about 0.25 mm to about 3 mm or from about 0.3 mm to about 1.5 mm. Aradius having a length from about 1 mm to about 4 mm may define the arcof the concave exterior surface of the head. The cross-section of thehead may include at least two convex and at least two concave exteriorsurfaces, where the cross-section of the head has a maximum diameterfrom about 0.25 mm to about 2.8 mm and a minimum distance from about 0.1mm to about 1.5 mm. The cross-section of the head also may include atleast two convex and at least two concave exterior surfaces, thecross-section of the head having a ratio of the maximum diameter to theminimum distance of from 30 to 0.17. The cross-section of the pin headmay have a maximum diameter from about 2 mm to about 3 mm, a minimumdistance from about 1 mm to about 1.5 mm, and a maximum arc distancefrom about 1.3 mm to about 1.4 mm, where a radius defines the arc of theconcave exterior surface and the radius has a length from about 3 mm toabout 4 mm.

A microdeposition pin also may include a shaft terminating in a headhaving a polygonal cross-section with at least one convex exteriorsurface and at least one substantially flat exterior surface. The pinmay have at least three substantially flat exterior surfaces or may haveat least two convex exterior surfaces and at least two substantiallyflat exterior surfaces. The substantially flat exterior surface mayextend from about 2 mm to about 8 mm from the head of themicrodeposition pin along a longitudinal direction of the shaft. Theshaft may taper toward the head or the shaft may have substantially thesame radius as the head. The pin may have a maximum cross-sectional headdiameter from about 0.25 mm to about 3 mm or from about 0.3 mm to about1.5 mm. The cross-section of the head may include at least two convexand at least two concave exterior surfaces, where the cross-section ofthe head has a maximum diameter from about 0.25 mm to about 2.8 mm and aminimum distance from about 0.1 mm to about 1.5 mm. The cross-section ofthe head also may include at least two convex and at least two concaveexterior surfaces, the cross-section of the head having a ratio of themaximum diameter to the minimum distance of from 30 to 0.17.

A biosensor may include a substrate having at least one raised featureand at least one reagent composition deposition on the raised feature,the deposition including an active biomolecule having a weight averagemolecular weight from about 10,000 to about 500,000, where the spread ofthe reagent composition beyond the raised feature is at most 0.3 mm. Thedeposition may include an active biomolecule having a weight averagemolecular weight from about 100,000 to about 400,000, and the activebiomolecule may include an active enzyme. The active enzyme may includeamine functional groups capable of hydrogen bonding interactions. Thesubstrate may be plastic and may include raised features having anaverage height above a top surface of the substrate of from about 5 μmto about 25 μm or of at most 5 μm.

The raised feature of the biosensor may be rectangular in shape as maybe the deposition. The deposition may be non-circular in shape. Theraised feature may be electrically conductive and the deposition mayspan from about 0.5 mm to about 3 mm of the longitudinal length of theraised feature. The raised feature may have a width of at most 1.5 mm ormay have a width of from about 0.2 mm to about 1.2 mm. The averagethickness of the deposition may be from about 1 μm to about 2 μm and mayinclude from about 0.02 μL to about 5 μL of the reagent composition. Themaximum length of the deposition may be from about 0.15 mm to about 3.2mm or may be from about 0.6 mm to about 1.0 mm. The deposition mayinclude at least one binder having a weight average molecular weightfrom 10,000 to 900,000 and may spread beyond the raised feature by atmost 0.15 mm. The deposition may have a substrate spread of at most 20%,of at most 8%, from 1% to 4%, from 1% to 2%, or essentially 0%.

A method of making a biosensor includes forming at least one raisedfeature on a substrate and depositing at least one reagent compositionon the raised feature, the reagent composition including an activebiomolecule having a weight average molecular weight from 10,000 to500,000, where the spread of the reagent composition beyond the raisedfeature during the depositing is at most 0.3 mm. The depositing mayinclude contacting at least one microdeposition pin to the raisedfeature. The deposition pin may be one of the deposition pins previouslydiscussed. The percent spread distance of the reagent composition froman exterior arc line of the microdeposition pin during the depositingmay be from about 5% to about 15% or from about 5% to about 10% withrespect to the length of the exterior arc line.

The depositing may include contacting at least one microdeposition pinhaving a polygonal cross-section with at least one concave surface tothe raised feature. The depositing may include contacting at least onemicrodeposition pin having a polygonal cross-section with at least oneconvex and at least one substantially flat surface to the raisedfeature. The deposited reagent composition may have a viscosity fromabout 1 cp to about 100 cp or from about 1 cp to about 20 cp. Thedepositing may include flowing the reagent composition on an exteriorsurface of the microdeposition pin, channeling the reagent compositiontoward a center of the microdeposition pin, forming an initialdeposition site on the substrate, and/or configuring an initialdeposition site in response to an exterior surface of themicrodeposition pin.

Other systems, methods, features and advantages of the invention willbe, or will become, apparent to one with skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 represents a cross-section of a contact surface of a conventionalround microdeposition pin.

FIG. 2 represents a cross-section of a deposition pin having the samemaximum diameter as the pin of FIG. 1, but with two substantially flatsurfaces and two convex surfaces.

FIG. 3A illustrates an embodiment of a microdeposition according to thepresent invention.

FIGS. 3B-3C are illustrations of a partial side view and bottom view,respectively, of the embodiment of FIG. 3A.

FIG. 4 is a top view of an image depicting reagent compositiondepositions made using the microdeposition pin of FIG. 3A.

FIGS. 5-6 are images depicting reagent composition depositions madeusing the microdeposition pins of FIGS. 1 and 2, respectively.

FIGS. 7-13B illustrate alternate embodiments of microdeposition pins ofthe present invention.

FIG. 14 is a schematic diagram of an embodiment of a contact surface ofa pin according to the present invention.

FIG. 15 illustrates a holder including multiple microdeposition pins.

FIG. 16 represents a method of forming a biosensor.

DETAILED DESCRIPTION

A microdeposition system for a biosensor has one or more microdepositionpins with contact surfaces having a polygonal cross-section and one ormore concave exterior edges. The microdeposition pins reduce thespreading of a reagent composition away from the concave edge inrelation to substantially flat or convex exterior edges. Microdepositionsystems with microdeposition pins having polygonal contact surfaces andone or more substantially flat exterior edge also reduce the spreadingof the reagent composition away from the substantially flat edges inrelation to convex exterior edges. Thus, in addition to size and reagentcomposition morphology, the shape of the contact surface of themicrodeposition pin may be used to alter spreading of the reagentcomposition. Contact surfaces having concave edges also may provideexternal reagent composition reservoirs to a solid microdeposition pin.

The present invention will be discussed with reference to creating abiosensor by depositing a reagent composition. However, the presentinvention is equally adaptable to forming most microarrays created usingmicrodeposition.

Conventional contact surface 2 of pin 100 used in pin-deposition isillustrated in FIG. 1. Pin 100 has a circular contact surface 2, knownto create substantially circular footprints when employed duringpin-deposition. A further discussion regarding the resultant footprintof the contact surface 2 will be discussed below.

As shown in FIGS. 3A-3C, a first aspect of the present inventionincludes a microdeposition pin 10 having a shaft 12, a mounting collar14, and a head 16. The shaft 12 is illustrated having a taperedcross-section extending from a first end 18 of the shaft to a second end20. But the shaft 12 may also have a constant radius throughout itslength or may have other geometric cross-sections throughout its lengthwithout deviating from the scope of the present invention. Thus, theradius of the shaft 12 may remain substantially constant, may changeconstantly to provide a taper, or may change abruptly, as illustrated inFIG. 3A.

The collar 14 is attached to the first end 18 of the shaft 12 andextends outwardly therefrom. The collar 14 may be integrally formed withthe shaft 12 or attached thereto using methods known to those in theart. The collar 14 may be employed to connect the pin 10 to a holder, aswill be discussed below.

As shown in FIG. 3A, the head 16 of the pin 10 extends outwardly fromthe second end 20 of shaft 12. The head includes a base 22, a contactsurface 24 and side surfaces 26. The base 22 is in communication withthe shaft 12, while the contact surface 24 is remote from the shaft.

A more detailed illustration of head 16 will be discussed with referenceto FIGS. 2 and 3B-3C. As previously mentioned, the head 16 includes abase 22, a contact surface 24 and side surfaces 26. The side surfaces26, which include first side wall 26A, second side wall 26B, third sidewall 26C and fourth side wall 26D, extend between the base 22 andcontact surface 24 thereby connecting the two. As shown in FIGS. 2 and3B-3C, the side walls 26A-26D may be substantially vertical.

The side walls 26A-26D abut the contact surface 24 at edges 28A-28D,respectively. The edges 28A-28D define the outer boundary of contactsurface 24. As shown in FIG. 3C, edges 28A and 28B are concaved, whileedges 28C and 28D are convexed. As shown in FIG. 2, edges 28A and 28Bare substantially flat, while edges 28C and 28D are convexed. Theconcave or substantially flat edges 28A and 28B help control the flow ofbiochemical material as the head 16 of the pin 10 contacts a substrate.

The contact surface 24 of pin 10 has a maximum diameter D, illustratedby dotted line 40, passing through the center of the surface. Themaximum diameter D is the distance between the two farthest pointspositioned on the perimeter of a cross-section of the contact surface24.

FIG. 4 illustrates the deposition result when using a reagent with thepin 10 of FIG. 3C described above in conjunction with a substrate 50.The contact surface of the pin used to create the deposition result ofFIG. 4 had a maximum diameter of approximately 2.4 mm. The substrate 50includes electrical conductors 52 defining a first target area 54 and asecond target area 56 separated by portions of the substrate 50. The topand bottom portion of the electrical conductors in each of the firsttarget area 54 and second target area 56, as well as portions 60A and60B of the substrate 50, positioned adjacent the top and bottom of theconductors 52 in FIG. 4 were masked with a layer of dielectric to limitexposure at locations where the reagent spreading was not critical. Incontrast, portions 62A of the substrate that are more centrally locatedrelative to the targets areas 54, 56 and are critical areas, were notencumbered by a dielectric layer. The criticality of the locations isdependent on whether target areas are adjacent to one another. Forinstance, the side 54A of first target area 54 and the side 56A ofsecond target area 56 are critical because only a portion of thesubstrate 50 separates the conductors 52 in each target area 54, 56. Ifthe reagent was allowed to flow past the substrate 50 and electricallyconnect the first target area 54 to the second target area 56, thesensor would be less effective.

The spreading of the reagent proximate the portions 62A of the substrate50 after deposition is controlled by the concave edges 28A and 28B ofthe pin 10. The convex edges 28C and 28D at the top and bottom of thehead 16 of the pin 10 of FIG. 3C resulted in more reagent compositionspreading along the conductors 52 as compared to the concave edges 28Aand 28B.

A discussion of how the concave edges 28A, 28B of the head 16 of the pin10 help limit the outward spread of the reagent material such that amore controlled footprint can be achieved is illustrated with referenceto second target area 56 illustrated in FIG. 4. The second target area56 includes a dotted rectangular line DL having a first set 70 ofopposing side walls 70A and 70B along with a second set 72 of opposingside walls 72A and 72B. The dotted line defines a desired location forthe deposit of reagent deployed by pin 10. As the pin 10 contacts theconductor 52 to deposit the reagent the concave edges 28A and 28B arepositioned adjacent and between the first set 70 of opposing side walls70A, 70B. And the convex edges 28C, 28D of the head 16 are positionedadjacent and between with the second set 72 of opposing side walls 72A,72B.

As can be viewed in FIG. 4, adjacent the first set 70 of side walls 70A,70B the reagent does not flow past the dotted line DL due to the shapeof the concave edges. Further, the reagent actually forms asubstantially straight line adjacent the location of where the concaveedges 28A, 28B contacts the conductor 52. In contrast, the reagent thatis deposited adjacent the convex edges 28C, 28D tends to flow past thesecond set 72 of side walls 72A, 72B of dotted line DL.

In fact, the reagent composition did not spread from the conductors 52onto the substrate 50 adjacent the first set 70 of side walls 70A, 70B.This reduction in spreading was observed even as the maximum diameter ofthe pins increased from about 1.6 to about 2.4 mm to provide a longerdeposition area along a conductor. Thus, the spreading of the reagentcomposition from raised rectangular features—the conductors 52—of thesubstrate 50 may be controlled using deposition pin heads that include aconcave edge along its contact surface.

This is particularly evident when comparing the reagent footprint ofFIG. 4 created using pin 10 of FIG. 3C to a footprint made using aconventional pin head. For example, conventional pin 100 of FIG. 1 wasused to create the reagent footprints of FIG. 5. The reduction inspreading provided by the concave edge may also be seen from the reagentfootprint of FIG. 6, which was made with a pin having substantially flatedges, such as seen in FIG. 2. It should be noted that the contactsurface 2 of pin 100 (FIG. 1) has a maximum diameter 4 that issubstantially equal to the maximum diameter 40 of the contact surface 24of pin 10 (FIGS. 2 and 3 c). And in all three scenarios the reagentcomposition deposited had a viscosity from about 2 to about 20centipoise (cp), as determined with a Brookfield Model DV3 Viscometerequipped with an ULA assembly for measuring reagent compositions havingviscosities lower than 300 cp. Viscosity measurements were performed atroom temperature with the instrument temperature set to 25° C. Themeasurements were performed at shear rates of 50, 100, 200 and 300 cps(cycle per second) to provide an indication of whether the compositionis sheared thin or thick. A 100 mM phosphate buffer solution was used asa control, which typically gave viscosity readings in the range of about1 to about 1.3 cp under different shear rates.

With attention to FIG. 5 it can be viewed that the substantiallycircular contact surface 2 of pin 100 left a first footprint 84 and asecond footprint 84A that are substantially circular. Each footprint 84,84A is highlighted by a dotted line. As a result of the reagentspreading, both of the footprints 84, 84A spread across a portion of thesubstrate 80 and into contact with one another, thereby corrupting thesensor. Similarly, as shown in FIG. 6, the footprints 88, 88A createdusing pin of FIG. 2 also spread from conductors 92, 92A to a portion ofa substrate 90.

By selectively controlling the spread of the reagent composition awayfrom the microdeposition pin, the flow of the reagent composition awayfrom the deposition target area may be reduced. Thus, biosensors mayinclude sensor strips having raised substrate features with limited orno spreading of the reagent composition beyond the features. The sensorstrips may have substantially rectangular shaped depositions of areagent composition including active biomolecules on the features. Theraised substrate features may be conductors providing electricalcommunication between the sample and the measurement device.

As shown in FIGS. 7-10, the head of the pin may have many differentshapes. For example in FIG. 7, the contact surface 124 of the pin 110includes first and second concave edges 128A, 128B and adjacent straightedges 128C, 128D. As mentioned with regard to FIG. 2, the straight edgestend to leave reagent footprints that are arcuate. FIG. 8 illustrates apin 210 with a contact surface 224 having a substantially triangularshape defined by three concave edges 228A, 228B and 228C. The edges228A, 228B and 228C are defined by the intersection of each sidewall226A, 226B and 226C and contact surface 224.

FIGS. 9 and 10 illustrate pins 310, 410 having contact surfaces 324, 424that have other polygonal shapes. In pin 310 the contact surface 324 hasfour concave edges 328A, 328B, 328C and 328D. And in pin 410, thecontact surface 424 includes concave edges 428A-428F. Although not shownin the figures, the contact surface of a pin may have any combination ofconcave edges, straight edges, convex edges or other geometric shapesthat include at least one concave edge without deviating from the scopeof the present invention.

Further, although the side walls of each of the pins have beenillustrated as substantially vertical, the side walls may be slantedand/or concaved. For example, with reference to FIG. 11, pin 510includes a contact surface 524 intersecting with slanted concave walls526A, and 526B. Each of the side walls 526A, 526B intersect the contactsurface 524 at a concave edge 528A, 528B. Although the side walls areillustrated as slanting outwardly they may slant inwardly. Once again,any combination of slanted and/or concaved walls, as well as convexedside walls may be employed without deviating from the scope of theinvention.

As shown in FIG. 12, a pin 610 may include a contact surface 624 and asample channel 630 for acting as a reservoir. The sample channel 630 maybe created and employed using methods known to those in the art.

Concave edges/side walls as well as sidewalls reduce the spread of thereagent composition. They may be selected to reduce the spread of thereagent composition to form an essentially straight edged or othershaped reagent composition deposition on a sensor strip. They also mayact as a reservoir for the reagent composition. By providing themicro-deposition pin with one or more concave exterior edges, the spreadof the reagent composition away from the concave edge may be reduced inrelation to the spread of the reagent composition away from convex orsubstantially flat edges.

When a microdeposition pin contacts the substrate, the effect of gravityand the surface tension of the reagent composition cause the compositionto flow along the surface of the pin and onto the substrate. Thecomposition forms an initial deposition area on the substrate. Due tosurface tension and gravity, the reagent spreads outward from theinitial deposition site to form a more spherical shape on the substrate.The reagent spreads outward from the initial deposition site until thereagent essentially dries or solidifies. The flow of the reagent maystop before drying or solidification is complete because of theincreasing viscosity of the reagent composition due to drying orsolidification, or due to a balancing of the surface energy of thereagent composition.

The viscosity of the reagent composition may be selected to alter thespread from the initial deposition site. However, competing effects areinvolved. As the viscosity of the reagent composition increases, theflow rate of reagent composition from the microdeposition pin to thesubstrate may decrease, while the volume of reagent compositiontransferred to the substrate may increase due to a larger drop of thehigher viscosity composition adhering to the microdeposition pin. Thus,a lower reagent composition flow rate may require longer touchdown timesof the pin to the substrate to obtain a similar amount of reagentcomposition deposition on the substrate while if a larger volume of thereagent composition adheres to the pin, a shorter touchdown time maysuffice.

Flat and concave edges guide the reagent toward the center of the pin.The flat and concave surfaces also may guide the reagent to form aninitial deposition area with a shape responsive to the configuration ofthe contact surface of the pin. When the reagent composition is guidedmore toward the center of the pin, the spreading of reagent on thesubstrate starts from a smaller and/or shaped initial deposition site,thus reducing or controlling the spread of the reagent composition onthe substrate. The shape of the initial deposition site may becontrolled by the shape of the microdeposition pin's contact surface,e.g., a triangular contact surface makes a triangular footprint. Then,as the reagent flows on the substrate from the pin, the reagentcomposition “fills” in the concave portions and may provide a depositionhaving substantially straight edges.

FIGS. 13A-13B illustrate a perspective and side view, respectively of amicrodeposition pin 710 having a shaft 712, a mounting collar 714, and ahead 716. Unlike the pin 10, the mounting collar 714 is of smallerradius than the shaft 712 to which it is attached. The head 716 includesconvex side wall 723 having a smaller radius than shaft 712. The head716 also includes a concave side wall 726.

The concave side wall 726 extends from the contact surface 724 to afirst end 718 of the shaft 712. The concave side wall 726 may extend anydistance from the contact surface 724 to the shaft 712 or may endsomewhere along the longitudinal axis of the head 716 either graduallyor abruptly. For example the concave side wall 726 may longitudinallyextend from about 2 mm to about 8 mm, and more preferably about 6 mm,from the contact surface 724 to the shaft 712. The length and angle ofthe arc of the concave side wall 726 may remain constant or may decreaseor increase when approaching the contact surface 724 and hence concaveedge 728. When the length of the arc of the concave side wall 726decreases toward the contact surface 724, a smaller cross-sectionalconcave edge is provided. And the concave side wall 726 may retain morereagent composition farther from the contact edge 728. In this manner, alarger external reservoir for the reagent composition may be created,while the desired ratio of concave to convex cross-sectional diametersmay be maintained.

FIG. 14 illustrates a cross-section of a contact surface 824 of a pin810 having a maximum diameter 890 with the two concave edges 828A, 828Band the two convex edges 828C, 828D. Radius 860 of circle 862 defines anarc of the concave edges 828A, 828B. Other arcs may be used. A minimumdistance 870 is the distance between interior arc lines 875 and definesthe closest portions of the arcs of the concave edge 828A, 828B. Maximumarc distance 880 is the distance between exterior arc lines 885 anddefines the farthest portions of the arcs of the concave edges 828A,828B. For example, a microdeposition pin tip may have a cross-sectionalmaximum diameter of about 2.4 mm. The radius defining the arc of theconcave surface may be from about 1.2 mm to about 5 mm. A radius ofabout 5 mm may provide substantially flat exterior edges. For concaveedges, a radius from about 1 mm to about 4 mm may be preferred. When thecross-sectional maximum diameter of the microdeposition pin tip is about2.4 mm and the radius defining the arc of the concave edges is about 3.7mm, the microdeposition pin may have a minimum distance of about 1.1 mmand a maximum arc distance of about 1.3 mm to about 1.4 mm. While aparticular configuration of the tip is shown, the tip may have otherconfigurations including those with different or asymmetricalcross-sections and those having one or more concave exterior edges.

When depositing the reagent composition on a substrate, the spread ofthe reagent composition in a direction perpendicular to the curvature ofa concave edge may be reduced. The concave edges may be configured tocontrol the spread of the reagent composition to obtain a desired edgeor shape of the deposition on the substrate of a sensor strip. Whileparticular concave edges are shown, the concave edge may have otherconfigurations including angular, curvilinear, a combination thereof, orthe like. Spread distance 887 is the distance the reagent compositionspreads outward from the exterior arc line 885 when deposited on thesubstrate. The spread distance 887 may be expressed in terms of length,percent, or the like. The percent spread may be the percentage of thespread distance 887 over arc distance 889 as defined between the ends ofthe arcs along the exterior arc line 885. Preferable percent spreads forthe reagent composition are from about 5% to about 15% and morepreferably from about 50% to about 100%. Other percent spread distancesmay be used.

The microdeposition pins may have a maximum cross-sectional contactsurface diameter from about 0.25 mm to about 3 mm and preferably fromabout 0.3 mm to about 1.5 mm. Other maximum cross-sectional diametersmay be used. When the cross-section of a pin's contact surface includesat least two convex and at least two concave edges as previouslydescribed, the maximum diameter is located between the opposed convexedges and may be from about 0.25 to about 2.8 mm and more preferablyfrom about 0.3 to about 1.5 mm, although larger and smaller dimensionsare certainly within the scope of the present invention. The minimumdistance between the opposed concave edges may be from about 0.1 toabout 1.5 mm, and preferably from about 0.2 to about 0.9 mm. Otherminimum diameters may be used.

By altering the maximum cross-sectional diameter and/or the minimumdistance of the pins, the volume of reagent composition deposited witheach contact of the substrate may be varied. By altering the ratio ofthe cross-sectional maximum diameter to the minimum distance of thepins, the spread of the reagent composition and the shape of theresulting deposition may be varied. To provide rectangular depositions,ratios of maximum/minimum cross-sectional dimensions may be from 30(3/0.1) to 0.17 (0.25/1.5), and preferably from 7.5 (1.5/0.2) to 0.33(0.3/0.9). Other ratios of maximum/minimum cross-sectional dimensionsmay be used.

Microdeposition pins may be made from any suitably hard material, suchas metal, alloy, silicon, ceramic, plastic, or composite. Preferably,the pins are made from titanium. The shaft and/or the tip of the pin maybe treated or coated to alter chemical and/or mechanical properties ofthe surface. As an example, the tip may be treated with a fluorocarbonto alter hydrophilicity.

In addition to the size and shape of the microdeposition pins, themorphology of the reagent composition also affects the spread andthickness of the resulting deposition. The reagent composition may be inliquid, gel, gellular, colloidal, or other form and may include reagentsand optionally a binder. The reagent compositions may have viscositiesranging from about 1 cp to about 100 cp. More preferable reagentcompositions have viscosities ranging from about 1 cp to about 20 cp orfrom about 4 cp to about 10 cp. Reagent compositions with otherviscosities may be used.

The constituents present in the reagent composition may include binders,such as polymers; biomolecules, such as enzymes specific to an analytelike glucose oxidase; and electro-active molecules that mediate the flowof electrons between the first and second electrodes, such as theferrocyanide/ferricyanide redox couple. The reagent compositions mayinclude binders having molecular weights from 10,000 to 900,000, andpreferably from 30,000 to 300,000 (weight/average). Binders having othermolecular weights may be used. Molecular weights may be determined bysize exclusion chromatography (SEC), and are generally expressed asweight averages or number averages.

The binder is preferably a polymeric material that is at least partiallywater-soluble. The binder may form a gel or gel-like material whenhydrated. Suitable partially water-soluble polymeric materials for useas the binder may include poly(ethylene oxide) (PEO), carboxy methylcellulose (CMC), polyvinyl alcohol (PVA), hydroxyethylene cellulose(HEC), hydroxypropyl cellulose (HPC), methyl cellulose, ethyl cellulose,ethyl hydroxyethyl cellulose, carboxymethyl ethyl cellulose, polyvinylpyrrolidone (PVP), polyamino acids, such as polylysine, polystyrenesulfonate, gelatin, acrylic acid, methacrylic acid, starch, maleicanhydride salts thereof, derivatives thereof, and combinations thereof.Among the above binder materials, PEO, PVA, CMC, and HEC are preferred,with CMC being more preferred at present for biosensors. Other bindersmay be used.

The reagent compositions also may include biomolecules havingweight/average molecular weights from 10,000 to 500,000 and preferablyfrom 100,000 to 400,000 that maintain biological activity afterdeposition. Biomolecules may include active enzymes and biopolymers,such as nucleic acids, proteins, and peptides. Other biomolecules may beused. The biomolecules may include amine functional groups capable ofhydrogen bonding interactions. Unlike laser ablation and other methodsused in the semi-conductor industry to form small features, the presentmicrodeposition pins can form depositions including biomolecules thatmaintain their biological activity.

FIG. 16 represents a method 1600 of forming a biosensor. In 1610 thecontact surface of a microdeposition pin is dipped into one or morereagent compositions. In 1620, the pin is contacted with a conductor orfeature of a substrate. In 1630 at least a portion of the reagentcomposition from the pin is deposited on the substrate. For anelectrochemical biosensor, one or more conductors and or electrodes maybe formed on the substrate before, during, or after the deposition. Foran optical biosensor, one or more features may be formed on thesubstrate before, during, or after the deposition. The conductors orother features present on the substrate may be raised, having an averageheight of from about 5 to about 25 μm above the surface of thesubstrate. Features having an average height of less than about 5 μm orless than about 1 μm above the surface of the substrate also may bepresent. The term “average height” of a raised feature or deposition isused because the top surface may be uneven, having peaks and valleys.

To form the sensor strip of an electrochemical biosensor, a firstconductor terminating in a first area and a second conductor terminatingin a second area may be formed on a planar plastic substrate. The firstand second areas may be physically separated or together and may be inflow communication with the sample or a portion of the sample. Theterminus of each conductor may have the shape of its respectiveconductor or a different shape and may be present in a reservoir wherethe sample is held for analysis. The terminus of each conductor may beformed from the same material as the other portions of the conductor, orfrom a different material. Preferably, the terminus of each conductor isformed from a non-reactive material, such as carbon, gold, or platinum.As the conductors may establish electrical communication between thesample reservoir and the contacts for connection to the measurementdevice, they often are rectangular in shape.

Microdeposition pins may be used to apply a first regent composition onthe first conductor and a second reagent composition on the secondconductor. The reagent composition may be deposited on the termini ofthe conductors or closer to the contacts. Preferably, at least a portionof the first and second reagent compositions resides within the samplereservoir. The first and second reagent compositions may be the same ormay include different reagents to provide the first and secondconductors with different electrochemical characteristics. For example,the first reagent composition may be optimized to oxidize or reduce theanalyte, while the second reagent composition may be optimized totransfer electrons between the redox reaction of the analyte and theconductor surface.

The closer the spacing between the first and second conductor termini,the less the reagent compositions can spread from the termini and remainseparate. Thus, referring back to FIG. 5, for example, substantialoverlap of the different reagent compositions was observed. This overlapof the reagent compositions may reduce the benefits of optimizingdifferent reagent compositions for the different conductors. Thus, thesmaller the width of the substrate between the conductors, the lessreagent composition spreading may occur and maintain the desiredseparate chemistries at the two conductors.

As the longitudinal length of a conductor may run from the terminus tothe contacts, the reagent composition can span any length of theconductor. The reagent composition may span from about 0.5 to about 3 mmof the longitudinal length of the conductor. Preferably, the portion ofthe conductors where the one or more reagent compositions are depositedhas a width of at most 1.5 mm and more preferably of at most 1 mm. Theportion of the conductors where the one or more reagent compositions aredeposited may have a width of from about 0.2 mm to about 1.2 mm or morepreferably from about 0.3 mm to about 1 mm. The portion of theconductors where the one or more reagent compositions are deposited mayhave other widths. The average thicknesses of the deposited reagentcomposition may range from about 1 μm to about 2 μm when using fromabout 0.02 μL to about 5 μL of a reagent composition having a viscosityfrom about 2 cp to about 10 cp and a maximum pin diameter from about 0.3mm to about 2.5 mm. Other thicknesses of the deposited reagent may beused.

The reagent composition may spread at most 0.3 mm, at most 0.15 mm, orat most 0.05 mm beyond the conductor. The spread of the reagentcomposition away from the conductor surface and onto the substrate alsomay be defined as percent substrate spread by dividing the distance thereagent composition spreads onto the substrate by the width of theconductor. Thus, a reagent composition spread of about 0.1 mm beyond aconductor having an about 1 mm width gives an about 100% substratespread. The sensor strips may have reagent composition substrate spreadsof at most 20%, preferably at most 15%, and more preferably at most 8%.The reagent composition substrate spreads may range from about 1% toabout 4% or more preferably from about 1% to about 2% are preferred. Thereagent composition may not spread on the substrate, thus providing anessentially 0% substrate spread. Other reagent composition substratespreads may be used.

In another aspect of the present invention, a holder 970 may be providedso as to employ multiple pins 910 simultaneously. For example, as shownin FIG. 15, multiple pins 910 may be combined in a holder 970, toprovide multiple depositions with one contact of a substrate (not shownin the figure). The holder 970 may be attached to a motion controlsystem (not shown) for automated movement of the microdeposition pins inmultiple dimensions. The microdeposition pin 910 may be fitted withmounting collars, such as collar 14 as represented in FIG. 3A, to assistin affixing multiple pins in the holder 970.

While various aspects of the present invention have been described, itwill be apparent to those of ordinary skill in the art that otherembodiments and implementations are possible within the scope of theinvention.

What is claimed is:
 1. A microdeposition pin, comprising: a shaftterminating in a head, the head having: a base, a contact surfaceincluding at least two convex and at least two concave edges, thecross-section of the contact surface having a maximum diameter betweentwo convex edges from about 0.25 mm to about 3 mm, having a minimumdistance between two concave edges from about 0.1 mm to about 1.5 mm,and having a ratio of the maximum diameter to the minimum distance offrom 7.5 to 0.33, and side surfaces connecting the base to the contactsurface and including a concave side wall.
 2. The pin of claim 1,wherein said contact surface further includes a flat edge.
 3. The pin ofclaim 1, wherein said side surfaces include a first side wall that isapproximately perpendicular to said contact surface.
 4. The pin of claim1, wherein said side surfaces include a first side wall that is angledrelative to said contact surface of the pin.
 5. The pin of claim 1,wherein said side surfaces include a concave side wall intersecting saidcontact surface to form one of the concave edges, wherein said concaveside wall extends substantially the length of said head.
 6. The pin ofclaim 1, wherein said side surfaces include a concave side wallintersecting said contact surface to form one of the concave edges,wherein said concave side wall is tapered along a length of said head.7. The pin of claim 1, wherein said head includes a channel thereinterminating at an aperture disposed at said contact surface.
 8. The pinof claim 1, further comprising a collar remote from said head of saidpin, said collar adapted for affixing said pin to a holder.
 9. The pinof claim 1, the cross-section of the contact surface having the maximumdiameter from about 2 mm to about 3 mm, the minimum distance from about1 mm to about 1.5 mm, and a maximum arc distance from about 1.3 mm toabout 1.4 mm, where a radius defines the arc of at least one of theconcave edges, and the radius has a length from about 3 mm to about 4mm.
 10. An apparatus for the deposition of a reagent composition, theapparatus comprising: at least one microdeposition pin comprising: ashaft terminating in a head, the head having: a base; a contact surfaceincluding at least two convex and at least two concave edges, where thecross-section of the contact surface has a maximum diameter between twoconvex edges from about 0.25 mm to about 3 mm, has a minimum distancebetween two concave edges from about 0.1 mm to about 1.5 mm, and has aratio of the maximum diameter to the minimum distance of from 7.5 to0.33; side surfaces connecting the base and the contact surface andincluding a concave side wall; and a holder for grasping said at leastone microdeposition pin such that said contact surface is remote fromsaid holder.
 11. A method of forming a reagent composition footprint,comprising: depositing an amount of the reagent composition onto acontact surface of a pin, said contact surface having at least twoconvex edges and at least two concave edges, where the cross-section ofthe contact surface has a maximum diameter between two convex edges fromabout 0.25 mm to about 3 mm, has a minimum distance between two concaveedges from about 0.1 mm to about 1.5 mm, and has a ratio of the maximumdiameter to the minimum distance from 7.5 to 0.33; and engaging saidcontact surface of said pin with a substrate to form a reagentcomposition deposition on the substrate, the reagent compositiondeposition comprising a footprint having at least one substantiallystraight edge.
 12. The apparatus of claim 10, wherein said at least onemicrodeposition pin includes a plurality of microdeposition pins,wherein each pin includes a contact surface having at least two convexand at least two concave edges; where the cross-section of the contactsurface of each pin has a maximum diameter between two convex edges fromabout 0.25 mm to about 3 mm, has a minimum distance between two concaveedges from about 0.1 mm to about 1.5 mm, and has a ratio of the maximumdiameter to the minimum distance of from 7.5 to 0.33.
 13. The apparatusof claim 12, where the cross-section of the contact surface of each pinhas the maximum diameter from about 2 mm to about 3 mm, the minimumdistance from about 1 mm to about 1.5 mm, and a maximum arc distancefrom about 1.3 mm to about 1.4 mm, where a radius defines the arc of atleast one of the concave edges, and the radius has a length from about 3mm to about 4 mm.
 14. The apparatus of claim 10, where the cross-sectionof the contact surface has the maximum diameter from about 2 mm to about3 mm, the minimum distance from about 1 mm to about 1.5 mm, and amaximum arc distance from about 1.3 mm to about 1.4 mm, where a radiusdefines the arc of at least one of the concave edges, and the radius hasa length from about 3 mm to about 4 mm.
 15. The method of claim 11,where the reagent composition deposition comprises a footprint having atleast two substantially straight edges.
 16. The method of claim 15,where the reagent composition deposition is rectangular in shape. 17.The method of claim 15, where the deposition has a length of from about0.15 mm to about 3.2 mm, and a width of from about 0.2 mm to about 1.2mm.
 18. The method of claim 15, where the deposition has a thickness ofabout 1 μm to about 2 μm.
 19. A microdeposition pin, comprising: a shaftterminating in a head, the head having: a base; a contact surfaceincluding: a first convex edge; an opposing second convex edge; a firstconcave edge connecting the first and second convex edges at respectivefirst ends thereof; an opposing second concave edge connecting the firstand second convex edges at respective second ends thereof; and sidesurfaces connecting the base to the contact surface and including aconcave side wall that forms one of the first and second concave edges,wherein the cross-section of the contact surface includes: a maximumdiameter between the first and second convex edges from about 0.25 mm toabout 3 mm; and a minimum distance between the first and second concaveedges from about 0.1 mm to about 1.5 mm.
 20. The pin of claim 19,wherein the concave side wall is approximately perpendicular to thecontact surface.
 21. The pin of claim 19, wherein the concave side wallis tapered along a length of the head.
 22. The pin of claim 19, whereinthe head includes a channel therein terminating at an aperture disposedat the contact surface.
 23. The pin of claim 19, further comprising acollar remote from the head of the pin, the collar adapted for affixingthe pin to a holder.
 24. The pin of claim 19, the cross-section of thecontact surface having the maximum diameter from about 2 mm to about 3mm, the minimum distance from about 1 mm to about 1.5 mm, and a maximumarc distance from about 1.3 mm to about 1.4 mm, where a radius definesthe arc of at least one of the first and second concave edges, and theradius has a length from about 3 mm to about 4 mm.